A non-radiative dielectric (NRD) guide and a suspended stripline (SSL) are two types of prominent transmission media used for forming millimeter wave integrated circuits. Low loss and low production cost are two main factors that make NRD guides suitable for wireless communication applications at millimeter wave frequencies.
On the other hand, suspended striplines overcome the disadvantage of having to maintain tight dimensional tolerances as in rectangular waveguides, and incorporates the advantageous features of planar technology in the millimeter wave region. The circuits are compatible with beam lead and chip devices, thus offering a potential for construction of passive and active millimeter wave integrated circuits.
Furthermore, suspended striplines permit easy transition to standard rectangular waveguide, and other planar and quasi-planar transmission lines. These include the inverted microstrip, finline and coplanar lines. To utilize the inherent advantages of these two prominent millimeter wave integrated circuit technologies, it is necessary to develop a suitable transition between these two transmission media.
Several transition devices have been described for coupling an NRD guide to a stripline. The concept of a probe type transition between a stripline and an NRD guide was first proposed in 1990 in a paper titled “Analysis and Design of StripLine to NRD Guide Transition” in Asia-Pacific Microwave Conference Proceedings. Other successful efforts to integrate an NRD guide with planar transmission lines, such as a microstrip line, coplanar line or slot line have been reported in 1996. In these reported works, a transition from a microstrip to an NRD guide is proposed and some active and passive components useful for developing hybrid NRD guide systems are reported. However, these papers do not describe a transition from an NRD guide to a suspended stripline (SSL).
WO 02/067366A1 describes a transition from an SMA connector to an NRD guide. Modified SMA connectors are available in the market for connecting a SSL to an SMA connector. However, such transitions provide very poor performance in terms of repeatability of the transmission coefficient. The higher-performance K-connector is not so suitable as it has an impact on the low-cost nature of NRD-guide components.
Also, depending on the tolerances held during manufacturing, SMA connectors have an upper frequency limit which is anywhere from 18 to 26 GHz. This is highly undesirable for microwave communication applications using signals having frequencies higher than 18 GHz. A feed line is inserted between the NRD guide and the SMA connector to transmit TEM waves, and a mode suppressor is added in the middle of a bisected NRD guide for suppressing undesirable modes. This leads to additional hardware requirements in the coupling device, as an SMA connector, a feed line and a mode suppressor are required.
U.S. Pat. No. 5,987,315 describes a diode circuit in a dielectric waveguide device, and a detector and a mixer used within the diode circuit. A diode circuit in the dielectric waveguide is designed to improve the facility with which a circuit substrate is mounted in the dielectric waveguide, and to make matching between a dielectric waveguide and a diode easier.
A conductor pattern (forming a stripline) is disposed so as to intersect a pair of dielectric strips substantially perpendicularly to the same, and two filter circuits are fabricated on opposite sides of the dielectric strips, thereby forming a resonant circuit. However, the device is used specifically for diode devices and requires suspending a conductor pattern on a circuit substrate between conductor plates by passing the circuit substrate through the dielectric strip to form a suspended stripline.
The device does not provide proper protection for the circuit substrate, which is left suspended through the dielectric strip. Also, the device requires extra filters on opposite ends and extra diodes to prevent propagation of undesirable electromagnetic wave modes through the suspended stripline. Hence, extra hardware is required. The device also does not provide proper protection against external electromagnetic wave sources.